During the manufacture of an integrated circuit device, a lithography process is used to form a circuit pattern on a wafer. In the lithography process, a photomask is used to transfer a desired pattern onto a substrate. Recently, as the design rule of semiconductor devices has reduced, the wavelength of light that is used during an exposure process tends to decrease. Accordingly, extreme ultraviolet (EUV) light having a short wavelength is used during an exposure process. During EUV lithography, when an EUV photomask that is not protected from pellicles is used, the EUV photomask may be polluted by foreign materials such as a carbon-containing material or particles, and thus, the polluted EUV photomask typically requires cleaning. Moreover, as a cleaning process for removing a contaminant on a photomask is repeated at regular intervals, the structure of an EUV photomask may be damaged, or a critical dimension (CD) of patterns included in the EUV photomask may change undesirably.